Measurements of vector-boson production in ATLAS and CMS

Manuella G. Vincter (Carleton University) presenting results from

ATLAS, CMS, LHCb, CDF, and D0

u u d

u u d

Electroweak interactions W-

W+

2

10-4 1 x1

x𝐮� u

Parton distribution functions f of the proton (pdf) x1,x2 = momentum fraction of partons 10-4 1 x2

xuv u

Thanks to: desy.de, hepdata.cedar.ac.uk

3

10-4 1 x1

x𝐮� u

Parton distribution functions f of the proton (pdf) x1,x2 = momentum fraction of partons

Z/γ*

q,g

10-4 1 x2

xuv u

σ=∑ ∫𝒅𝒅𝟏𝒅𝒅𝟐 𝒇𝒂(𝒅𝟏,𝑸𝟐) σ�𝒂,𝒃,𝒌(𝒅𝒂,𝒅𝒃)𝒂,𝒃,𝒌

𝒇𝒃(𝒅𝟏,𝑸𝟐)

Hard scattering σ� for kth sub-process between partons of flavour a and b

q q

Z/γ* g

(+ other diags…)

Thanks to: desy.de, hepdata.cedar.ac.uk

Via hard scatter, can produce massive EW states in 𝑝𝑝/𝑝�̅� collisions

SM Z, W, t production EW interactions at TeV scale pQCD

Global fits to extract PDFs

Feed e.g. W±, Z/γ*, … cross section information into global fits to extract PDFs All data have differing sensitivity to different aspects of the proton’s PDFs. EW boson production sensitive to valence and sea quark distributions

4

Parameterise PDFs: xg(x) = AgxBg(1-x)Cg+… xuv(x)= … xdv(x)= … xu(x) = ... xd(x) = … xs(x) = … xs(x) = …

Rapidity y (related at LO to momentum fraction x)

𝑍~ 0.29 𝑢𝑢� + 𝑐𝑐̅ + 0.37(𝑑�̅� + 𝑠�̅� + 𝑏𝑏�)

𝑊+~ 0.95 𝑢�̅� + 𝑐�̅� + 0.05(𝑢�̅� + 𝑐�̅�) 𝑊−~ 0.95 𝑑𝑢� + 𝑠𝑐̅ + 0.05(𝑑𝑐̅ + 𝑠𝑢�)

Thanks to: M. Sutton Moriond 2014, U. Klein DIS 2012

xdv arXiv:1312.6283

5

??

New Physics Processes?

arXiv:1405.4123

Beyond the SM?

Searches for new dilepton resonances

γ Z

Z

Anomalous couplings of gauge bosons

New particles in this loop?

Outline of presentation

Single W, Z/γ* production Z/γ*: mll , yll dependence Lepton and W charge asymmetry mW

Multiple W, Z, γ production Neutral and charged aTGC VBS: W±W±jj production

Top physics Quark pair, single-top cross sections, |Vtb| Mass

Will show an illustrative experimental result per topic, but many of these measurements done at all experiments: D0, CDF, CMS, ATLAS (too many to show!)

6

SINGLE W, Z/γ* PRODUCTION

7

*

mll dependence of Z/γ* production

Very wide mass range measured at the LHC: mll~12-2000 GeV dσ/dmll, d2σ/dmll d|yll|

Measurements compared to fixed-order calculations like FEWZ, including higher-order EW corrections, and various PDFs PDFs: MSTW2008, HERADPDF1.5, CT10, CT10W,AMB11, NNPDF2.1,2.3, JR09, ABKM09, …

8

Low-mass DY: dominated by EM coupling of γ* to qq�

Different sensitivity to u, d-type qq� than on peak

Peak region and above dominated by Z, γ* coupling to qq�

High-mass DY shape can be modified by new physics

arXiv:1406.3660 CMS PAS SMP-14-003

yll and mll

CMS 7TeV: (1/σZ) dσ/dmll: ee+µµ channel normalised to peak region Comparisons including LO and NLO EW corrections

Dimuon (1/σZ) dσ/d|yll| normalised to peak region in mll bins compared to FEWZ using various PDF sets Test compatibility of PDFs with low-to-high-mass DY

Also ratio of born-level (1/σZ) dσ/dmll at 8TeV to 7TeV

9

JHEP12(2013)030

mll = 20-30GeV 60-120GeV 120-200GeV (low mass) peak (high mass)

LHC lepton-charge asymmetry

Dominant W production mechanisms at LHC: valence+sea antiquark: and W+,W- production asymmetry due to valence content

(CMS at 8TeV) Lepton charge asymmetry vs. pseudorapidity η can provide

information on PDFs: d/u ratio and sea antiquarks (including strangeness)

CMS measurement at 8TeV with W→µν and pTl>25GeV

Agreement with CT10, NNPDF2.3, HERAPDF1.5 Less so: MSTW2008 |η|<1 (MSTW2008CPdeut better)

LHCb measurement at 7TeV with W→µν and pTl>20GeV

Forward acceptance: unique rapidity coverage for PDFs Excellent agreement with NNLO + different PDFs

except at highest η where some predictions undershoot the data.

10

u u d

u u d

d�

W+ arXiv:1312.6283

ud�→W+ du�→W−

PRL112(2014)191802arXiv:1408.4354

X

Tevatron W charge asymmetry

Lepton charge asymmetry is convolution of W asymmetry and V-A structure of W decay Leptons at given η originate from a range of W rapidity yW and hence wide x range

D0 at Tevatron: use ν weighting method to extract W charge asymmetry Assuming mW value gives two possible solutions to missing information on pν

z, which can be partially resolved on a statistical basis from known V-A decay distributions, assigning probabilities to pν

z solutions 9.7fb-1 at √s=1.96TeV

Comparison to MC@NLO + NNPDF2.3, MSTW2008NLO

Good agreement except slight overshoot of predictions at low |yW| Expt uncert << NNPDF2.3 uncert

Results can significantly constrain PDF predictions

11

PRL 112 (2014) 151803

The mass of the W boson: mW

EW sector of SM relates important parameters such as mW, αEM, GF and sin2θW

Quantum corrections to mW dominated by contributions depending quadratically on the top mass mt and logarithmically on the Higgs mass mH

Precision measurements of mW were first used to predict mH before the Higgs was observed Now use comparisons of predicted mH to measured mH to look for new physics! Extraction of mW from hadron collisions

ud�→W+(→l+ν)+X → Can’t fully reconstruct the final state! Transverse plane balance: �⃑�T

ν=- �⃑�Tl - 𝑢T

Use variables sensitive to mW :

pTl , ET

miss, mT= 2 pTlpT

ν [1 − cos (ϕl − ϕν)]

12

e

pTl

ν pTν

pTW

Hadronic recoil 𝑢T

Simulate what these variables should look like as measured in the detector, scanning over a range of possible mW values

Perform a fit of these templates to data

Tevatron mW

Fermilab Tevatron measurements D0: W→eν, 4.3fb-1, 1.68M evts (+earlier 1fb-1) [PRD89 (2014) 012005, PRL108 (2012) 151804]

CDF: W→e,µν, 2.2fb-1, 1.10M evts [PRD89 (2014) 072003, PRL108 (2012) 151803]

Dominant expt sys: lepton E scale & hadronic recoil, dominant theo uncert: knowledge of PDF δmW

D0 = 23MeV, δmWCDF= 19MeV mW

Tevatron=80387±16MeV World avg: known to 15MeV!

13

CDF

Updated from

arXiv:1204.0042

mT pTe ET

miss

Future prospects for mW

Use global fits of EW sector of the SM to compare measured and predicted masses Incredible compatibility! mW, mt, mH

Even with precision of δmW = 15MeV, indirect determination of mW better by factor of ~2

Calls for better measurements Projected final Tevatron precision: δmW ~ 9MeV? Can LHC do better? A real challenge!

Higher pileup environment Momentum scale, recoil model, PDF

will need to be well known 14

http://project-gfitter.web.cern.ch/project-gfitter/

arXiv:1407.3792

Targets for LHC arXiv:1310.6708

Note on theo uncertainties on mass: ATL-PHYS-PUB-2014-015

MULTIPLE W,Z,γ PRODUCTION

15

Multiple Gauge-Boson Couplings

Test predictions of EW sector of SM at TeV scale Self interactions between gauge bosons

Will talk about anomalous Triple Gauge Couplings (aTGC) Anomalous quartic gauge boson couplings aQGC also being measured

SM diboson production is also a source of background for: Higgs production (e.g. H→WW, ZZ) Searches for new physics

Deviations: new resonances decaying to gauge bosons, other non-SM processes? At tree level, some TGCs are non-zero in the SM

γWW, WWZ Other TGCs are zero at tree level but have non-zero contributions at the higher loop levels

e.g. γZZ O(10-4) contributions at one-loop SM. Some BSM models are O(10-3-10-4) Precision measurements could reveal new physics! Will review processes with ZZ, WW, WZ, Wγ, Zγ final states

leptonic decays of W,Z (W→lν, Z→ll,νν)

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γ W

W

γ Z

Z

SM? BSM? New particles in this loop?

aTGC: nomenclature

Introduce a general V V’ V” vertex γWW, WWZ, Zγγ, ZZγ, ZZZ

Coupling nomenclature: Define couplings such that SM values are 0 or 1

For SM couplings that are 1: define deviation ∆ from SM

Test for any aTGC Note: Many terms in Lagrangian would give cross

sections as a function of √s leading to unitarity violation. As this is not possible, new physics interactions at scale Λ needed to counter the effect Use form factor parameterisation that leads to

couplings that vanish at high √s

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Charged

Couplings Vertex (Final state)

λγ, ∆κγ γWW (WW, Wγ)

λZ, ∆κZ, ∆g1Z ZWW (WW, WZ)

Neutral

Couplings Vertex (Final state)

h3γ, h4

γ γγZ (Zγ)

h3Z, h4

Z ZZγ (Zγ)

f4γ, f5γ γZZ (ZZ)

f4Z, f5Z ZZZ (ZZ)

V V”

V’

fiV =fi0

V/(1+�̂�/Λ2)𝑛

aTGC: methodology

Measure diboson production cross section vs. variables sensitive to aTGCs W →lν: pT

l Z →ll: m4l (ZZ) or pT

ll of leading Z Presence of aTGC would distort shape Use MC to reweight / interpolate to

distributions with anomalous couplings Set limits on aTGCs on each coupling:

assuming others are zero or on pairs assuming others are zero

18 The leading Z boson transverse momentum

JHEP03(2013)128

JHEP03(2013)128

Charged aTGC limits

19

WWγ,WWZ

LEP still sets stringent limits in some cases, LHC limits comparable to Tevatron

Snap shot of aTGCs: LHC 7TeV data + LEP + Tevatron

https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSMPaTGC

Neutral aTGC limits

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Zγγ, ZZγ, ZZZ

LHC is now dominating this measurement

→ No evidence for aTGCs

JHEP03(2013)128

Phys. Rev. D 87, 112003 (2013)

Vector boson scattering (VBS): W±W±jj

VBS VV→VV where V=W or Z: key process to probe nature of EW symmetry breaking Without a SM Higgs, longitudinally polarised VBS amplitude violates unitarity at ~1TeV! Newly discovered Higgs boson could unitarise process

V+V+jet+jet in final state → both EW and strong processes Same sign WW: EW process dominates

W±W±jj production: ATLAS 20.3fb-1 at 8TeV Enhanced VBS region: e±e± , µ±µ± ,µ±e±, + ≥2 well separated jets in |∆yjj|, high invariant mass mjj>500GeV

3.6σ significance of EW signal (σWW(VBS)) Deviations from SM quartic gauge couplings:

Parameterised by α4,α5 : limits set 21

W±

W±

q

q

Jet

Jet

Z/γ,W, H, 4-pt

PRL113 (2014) 141803

TOP PHYSICS

22

Top production and decay: the many properties

23

p 𝑝 or �̅�

(anomalous?) couplings → Vtb

Top properties → mass, width, charge …

𝑡𝑡̅ and single top → production cross sections

(differential too!) → new production mechanisms?

Polarisation, spin correlations, production asymmetries

Top quark pair production and decay

Top quark pair (𝑡𝑡̅) production is via the strong interaction

Top quark subsequently decays ~100% to W + b: 𝑡𝑡̅→W+W-𝑏𝑏�

W decays are hadronic or leptonic Dilepton channel: very clean but low rate Lepton+jets: clean and good rate Measure 𝑡𝑡̅ production cross section σ(𝑡𝑡̅)

Precise σ(𝑡𝑡̅) → measurement of SM parameters: mt and αS

New physics could be hidden? New production modes or decays?

SM predictions: Will be a trade off:

stats vs. sys

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←85% Tevatron 15%→ ←15% LHC 85%→

All jets ~45%

Lepton+jets ~45%

Dileptons ~10%

Z’(?)

𝒕′or 𝒕�? New heavy quarks? SUSY decays?

√s [TeV] σ(𝑡𝑡̅) (NNLO+NNLL) [pb] (mt=172.5GeV)

Uncert. [%]

2 7.35

~4-6% 7 177.3

8 252.8

13 824.2

x100

ICHEP2014

1989 2013

𝒕�̅�: dilepton

ATLAS simultaneous: 𝑡𝑡̅, WW, Z/γ*→ττ Dominant processes in eµ final state

Template fit over ETmiss, Njets

Normalisation 𝑡𝑡̅, WW, Z/γ*→ττ free pars

Tevatron Run II combined results

stat ≅ sys ≅ lumi → tot = 5.4%

LHC combination with first 8TeV results stat << sys ≅ lumi → tot = 3.5% 25

Njets=0 Njets≥1

NNLO

σ(Z/γ*→ττ) vs. σ(𝑡𝑡̅) Comparisons with PDFs

arXiv:1407.0573

PRD89 (2014) 072001

Combined results

Single-top production

Single-top production is via the EW interaction

Measure fundamental parameters of SM σsingle-top ~ |Vtb|2 → CKM and unitarity

Vtb measured at LHC, Tevatron: ~2-10% Background in Higgs and SUSY searches Sensitive to new physics?

26

t-channel Wt-channel s-channel

www-d0.fnal.gov/Run2Physics/top/top_public_web_pages/top_feynman_diagrams.html

SM prediction [pb] arXiv:1311.0283

√s [TeV]

t Wt s Tot.

2 2.08 (62%)

0.25 (7%)

1.05 (31%)

~3

8 87.8 (76%)

22.2 (19%)

5.55 (5%)

~115

14 248 (72%)

83.6 (24%)

11.86 (4%)

~343

Meas. precision

~10% LHC

~20% LHC

~20% Tevatron

W’, H+,?

Single top: t and s channel

t-channel: CMS @ 8TeV (19.7fb-1) Lepton + 2 jets (1 b jet) Template fit on the untagged jet

s-channel: CDF full run 2 9.5fb-1 l+jet and ET

miss+jet MVA discriminants sensitive to s-channel

27

JHEP06 (2014) 090

PRL 112 (2014) 231805

Tevatron: t-channel vs. s-channel: summary

BSM predictions: 4- quark generations, top-flavour model with new heavy bosons, top-pions, FCNC

Fermilab-CONF-14-370-E

Top mass

mt is a fundamental parameter: mW, mt, mH together test the consistency of the SM Many techniques to extract mt

Decay kinematic fits or likelihood compatibility with top hypo, template fit to reco mass Matrix element technique: D0 l+jet (full run 2, 9.7fb-1)

From kinematic info in the event, use LH technique per-event probability densities Calculate probability that each event results from a 𝑡𝑡̅ or bkg

Overall JES is calibrated by constraining in-situ mass of hadronically decaying W

World avg last March: same precision of <1GeV Some tension with most recent measurements

28

[0.43%]

PRL113 (2014) 032002

arXiv:1403.4427

Conclusions

Single and diboson production is interesting on so many levels Probes of

pQCD, PDFs, consistency of the SM mll,|yll| dependence of Z/γ* production, W charge asymmetry, mW

Underlying foundation of many new physics searches e.g. critical to better understand backgrounds and

PDFs for LHC at higher energy/luminosity Sensitive venues for new physics: aT/QGCs Top quark physics Tevatron and LHC: top factories

Top mass known to better than 1GeV Moving into realm of precision measurements of top (differential) properties, not limited by statistics

Precision top physics will be taken to a new level at future colliders!

29

ATLAS-CONF-2014-057

dσ(𝑡𝑡̅)/dpTt

ICFA 2014 – Beijing, China - Oct 2014 – Manuella G. Vincter (Carleton University, Canada)

PANIC 2014

ADDITIONAL MATERIAL

30

Z cross section vs. φη*

A better variable to probe low-pT Z: φη*

where (φ between 2 leptons) and (η between 2 leptons) Probes same physics as Z pT but with better

precision

Depends uniquely on direction of lepton tracks (which is better measured than their momenta)

Significant improvement in the understanding of electron track parameters in 2011/2012 really helped this analysis!

31

𝑝𝑇𝑍

𝑝𝑇l 𝑝𝑇l

𝑝𝑇𝑍≈ mZ φη*

Phys. Lett. B720 (2013) 32

pT dependence of Z/γ* production

Near Z pole mll=≅ 90GeV within a mass window of ~±25GeV dσ/dpT

ll , d2σ/dpTll d|yll|

32

Low pTll: region of ISR

and intrinsic kT of partons

modeled through soft-gluon resummation or parton showers (PS) e.g. ResBos

(NLO,NNLO)+NNLL

High pTll: region

dominated by radiation of high pT gluons/quarks

Sensitive to gluon PDF Modeled with fixed-

order calculations like FEWZ @NLO,NNLO & DYNNLO (with NLO,NNLO EW corrs) arXiv:1406.3660

A tool for tuning: pTll

ATLAS 7TeV: (1/σfid) dσfid/dpTll, inclusively in yll (ee and µµ)

FEWZ,DYNNLO (top), ResBos (bot) Parton-shower tunes: determine sensitivity of dσ/dpT

ll to PS models Include measurement of φη*, highly correlated to pT

Z but depends on direction of tracks (better measured than momenta)

e.g. compare POWHEG+PYTHIA8 new tune AZNLO with base tune 4C

Primordial kT and ISR cut-off have been tuned

Consistent tune with pTll and φη* in agreement within 2%

with data for pTll<50GeV

33

NNLO+NNLL NLO +NNLL

arXiv:1406.3660

𝑝𝑇𝑍≈ mZ φη*

Phys. Lett. B720 (2013) 32

PDF extraction in the HERAFITTER framework

Use HERA inclusive DIS data with LHC W data to better constrain PDFs, in particular valence and strange

ATLAS: HERA + [W+charm] Repeat HERAPDF1.5 fit making ~free while

constraining other params to HERAPDF1.5 fit results ~1 at starting scale Q2=1.9GeV2

CMS: HERA + A(η) + [W+charm] Adding A(η) improves valence precision, changes shape Free-s fit where dbar and sbar parameterised separately

RS , just below 1 Within framework, ATLAS&CMS strange fraction definition similar

at starting scale… RS & rs can be directly compared: ~consistent

34

xuv xdv

ATLAS: JHEP05 (2014) 068 CMS: arXiv:1312.6283